1. Field of the Invention
This invention relates generally to the field of carton folding, gluing and sealing and in particular to an improved apparatus and method for skiving, hemming and pre-sealing edges of liquid carton blanks with a vacuum hemmer apparatus.
2. Description of Related Art
Although carton blanks are formed from a wide variety of materials, this invention is related to the manufacture of cartons made from carton blanks having surface coatings of a thermoplastic material. The carton blanks generally are laminated with a paper board core and outer coatings of a high or low density polyethylene or other thermoplastic. The laminate may contain an optional barrier of metallic foil or other material that forms an essentially gas impermeable membrane.
In applications where a box is designed to store liquids or to store contents in a moist environment, overlapping the edges of a carton to form the box does not produce a longitudinal seam that maintains its integrity over an extended time interval for such applications. The conventional overlapped configuration exposes one edge of the paper board core that is the center of the laminate. If that edge lies inside the carton, the liquid contents can wick through the paper board core and eventually destroy the carton. Hence, it is important that the folded carton prevent such wicking in order to maintain the integrity of the longitudinal seam.
U.S. Pat. No. 5,236,408, issued Aug. 17, 1993 to Hugh A. McAdam, III, et al. and assigned to International Paper Box Machine Company, Inc. of Nashua, N.H., discloses related art and a method and apparatus for forming carton blanks into folded cartons with hemmed edges. A skiving apparatus removes a portion of a carton blank material at a predetermined area such as a first half of an edge portion. Then a folding apparatus folds the skived portion onto the blank, irons it, and then opens the hem to lie in a predetermined plane that intersects the plane of the blank. Superheated air activates a thermoplastic coating at the inner half of the edges adjacent to the skived portion of the area to be hemmed. Hemming and sealing apparatus seals the skived outer half of the edge portion fully onto the coating on the inner thermoplastic. However, during the hemming operation the blank is not securely held at the edge being hemmed.
U.S. Pat. No. 4,540,391 issued Sep. 10, 1985 to Carl J. Fries, Jr. and assigned to International Paper Company of New York, N.Y. discloses an apparatus for skiving and hemming one or more edges of a paperboard web or blank to improve the sealing qualities of a container made from paperboard. The blank is skived twice, once to define an oblique surface and once to make a flat skived surface. The latter is folded over the former and heat sealed to a heat sealable material adjacent the skived region, defining a wedge-shaped edge portion which is ironed to produce a substantially flat sheet. Fries, Jr. discloses the use of vacuum suction to remove debris material during the pre-hemming milling operation which accomplishes the skiving.
U.S. Pat. No. 4,682,977 issued Jul. 28, 1987 to Gerald W. Buxton and assigned to Paper Converting Machine Company of Green Bay, Wis. discloses an apparatus for folding spaced segments of web material such as diapers having intermediate side flaps overfolded in the crotch portion making use of a vacuumized continuously moving belt system for gripping one surface of a planar web. Vacuum is applied to the bottom surface of a continuous belt means by means of a plenum chamber and conduits coupled to a vacuum pump. Continuous belt is equipped with sprocket holes engaging pins on head and tail sprockets. The continuous inner belt is equipped with a number of cutouts which allow vacuum to be applied to portions of the web which are not to be folded so as to maintain it under control.